The invention relates to an ignition timing control device for a turbo-charged internal combustion engine which advances or retards the ignition timing as a function of the pressure in the intake manifold.
The ignition timing in internal combustion engines is normally controlled, in order to obtain optimal operating conditions, as a function of engine speed. It is desirable, however, especially in the case of engines in which air is provided under pressure to the engine cylinder, i.e. turbo-charged engines, that the normal ignition timing be further adjusted depending upon the instantaneous engine load conditions. This is especially desirable when the engine undergoes heavy load, where there would be a danger of pre-ignition. Under these conditions, it is desirable to retard the ignition timing to avoid knocking, even though this compromises the lower fuel consumption attained with advancing the engine timing.
An internal combustion engine of this type is described in U.S. Pat. No. 3,543,738, in which a servomotor acts on an ignition timing adjustment device designed to advance or retard the ignition timing under certain engine operating states. The servomotor is controlled by two comparison devices. One device, responsive to the ratio of engine speed and the pressure in the fuel manifold, provides a signal dependent upon engine load to retard the ignition timing under heavy load. The other controller, providing a control signal responsive to the ratio of the fuel manifold pressure and the air manifold pressure, compensates for lower intake air pressure as would occur when the turbo charger is not fully operative.